The present disclosure relates to a power supply apparatus and a power supply method, capable of using power output from an external power system and a battery module.
When the power supply from an external power system (referred to as a commercial power source, a grid, or the like) decreases by an accident, or the like, or when a power demand seasonally increases, the power demand becomes greater relative to the power supply, leading to a possibility of unexpected power interruption. Other than this case, a power interruption due to a torrential rain, a lightning strike, or the like, is presumed.
It is known in conventional arts that an uninterruptible power supply (hereinafter, referred to as UPS) is used to supply power to a computer and a peripheral device when power failure such as power interruption occurs. The known UPS, however, is effective against a brief power interruption and this merely serves to temporarily supply power to the computer and the peripheral device. Therefore, this is hardly sufficient for supplying residence-based power when a large-scale and long-time power interruption occurs. Furthermore, there is a problem that the UPS operates at the time of power interruption and is not applicable for decreasing residence-based power usage of the external power system, for example.
Recently, a residence-based larger-capacity power storage apparatus is put into practical use. By utilizing the residence-based power storage apparatus, it is possible to ensure power supply at the time of power interruption and thus to reduce the power demand and the power usage of the external power system. For example, one measures would be to reduce the supply of AC power from the external power system to compensate for power shortage by a power storage apparatus (refer to Patent Document 1 below). Furthermore, there might be a problem that residence-based power demand increases to exceed contracted power with a power supplier and a breaker operates to cut off the power. In this case, by supplying power output from a power storage apparatus, it is possible to avoid a situation in which the contracted power is exceeded.
In order to convert DC output of a battery module into AC power supply, a DC-AC inverter is normally used. In case of the UPS, a maximum load (device) value connectable to the UPS is defined as a rated capacity. Furthermore, a capacity (V/Ah) of the battery module included in the UPS is defined. For example, description of DC 12 V/7.2 Ah represents continuation of running DC 12 V/7.2 A for an hour.
For overload, protection is activated. The overload means a state in which a load factor exceeds 100%. The load factor is a ratio of load capacity to UPS rated output capacity. Normal operation is operation in a range where the load factor is 100% or below. Backup time at power interruption can be set longer when the load factor is lower. In general, UPS rated capacity is set in consideration of an expected load. In a recent residence, however, a great-power consumption device such as an electromagnetic cooker is increasingly used, leading to an increased possibility of occurrence of overload.
Exemplary overload protection operation uses a bypass circuit. The bypass circuit is provided, instead of a UPS system, to directly transmit system AC power to a load. In addition to the usage of protecting overload, the bypass circuit is also used at maintenance.
The battery module included in the UPS is connected with a semiconductor switching element (e.g., a field effect transistor (FET)) for cutting off the discharge current in order to prevent the battery from being damaged by excessive discharge current. Furthermore, the module is configured such that a fuse is blown out in a case where excessive discharge current flows.